Communication devices such as wireless devices are also known as e.g. User Equipments (UEs) terminals, mobile terminals, wireless terminals and/or mobile stations.
Wireless devices are enabled to communicate wirelessly in a wireless communications networks.
Wireless device may further be referred to as mobile telephones, cellular telephones, laptops, or surf tablets with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, with another entity, such as another device or a server. Also other wireless device types related to the Internet are relevant in this context, e.g., copying machines, printers, vehicles, home appliances, etc. It may be envisaged a large number of devices that benefit from wireless connectivity which are traditionally not seen as wireless communication devices.
D2D Communication
Device discovery is a well-known and widely used component of many existing wireless technologies, including ad hoc and cellular networks. Examples comprise Bluetooth, several variants of the IEEE 802.11 standards suite, such as WiFi Direct. The key technique used by these standards is to use specially designed beacon signals that devices broadcast so that nearby devices can detect the proximity of such beacon broadcasting devices. After having detected each other the devices may, if desired, initiate a communication session. This is typically done in a direct Device-to-Device (D2D) fashion, where the devices transmit data through direct signaling between each other. Alternatively, such a communication session could be performed through a network, e.g., a WCDMA, LTE or 802.11 network.
D2D communication often takes place in unlicensed spectrum, e.g., the Industrial, Scientific and Medical (ISM) band at 2.4 GHz. Such a band is typically divided in a number of channels, and the devices would typically not beacon or communicate over all channels simultaneously. Similarly, other devices typically use parts of the full band, i.e. a number of channels, such that different parts of the band experience different interference scenarios. E.g., a few channels of a band are interfered for a device, and a few other channels are not interfered for the same device. In this document an interfered channel for a device refers to a channel at which the received energy from signals not of interest to the device exceeds a certain threshold during a time interval.
WO2011/063845 shows a way of performing beacon signal broadcasting. The solution comprises selecting by a node capable of entering a D2D communication, a beacon channel for broadcasting such that the occurrence of collisions on the selection of the beacon channel is avoided. The beacon signal is then broadcasted on the selected channel.
In the unlicensed bands the transmit power is limited to a comparatively low value, as compared to wide area systems. Hence, devices that are relatively close to each other may experience different interference scenarios. It may be so that two devices that are close enough for initiating a D2D communication are interfered on different channels, respectively. It may even be so that there is no single channel available at which both devices experience an interference free situation.
It should be realized that embodiments herein are not limited to unlicensed bands or bands with low power. The above examples are given for illustrative purposes, and the similar interference scenarios may be valid in other bands using other typical power levels.